1. Field of the Invention
The present invention applies to the field of acquiring timing for radio systems having multiple terminals and, in particular, determining a frequency offset of received symbols to adjust a local oscillator.
2. Description of the Prior Art
In high capacity digital radio communication systems, timing, frequency, and phase must be accurately tracked. The more accurate the tracking, the higher the data rate can be and the lower the error rate can be. Tracking becomes more difficult when there are several radios communicating together on the same system. In a hub architecture, the hub must track each of the remotes which may each have different offsets in timing, frequency and phase. In a network of peers, all of the peers must track all of the different other peers.
Tracking can be made easier by providing all the radios with an extremely accurate reference clock, however, such clocks are expensive and still may not be synchronized. Typically, long training sequences are used at the beginning of each burst. The training sequence is made longer at the expense of transmitted data. A complex clock recovery algorithm commonly is also applied before the packet is demodulated. Tracking continues during the burst because the burst may experience an offset from the receiver clock that will affect phase and carrier frequency during the burst. This complexity requires substantial system resources and can limit system capacity.